1. Field of the Invention
The present invention relates to a dielectric ceramic composition comprising calcium, titanium, aluminium, niobium and oxygen, which is favorable for dielectric resonators for use in a microwave region of a few GHz zone.
The dielectric ceramic composition of the invention is used not only for dielectric resonators but also for substrates for microwave ICs, dielectric control rods, etc.
2. Description of the Related Art
With the recent tendency in the art toward highly integrated microwave circuits, desired are small-sized high-performance dielectric resonators for them. The requirements of dielectric ceramic compositions for such dielectric resonators are that their relative dielectric constant xcex5r is large, that the absolute value of the temperature coefficient xcfx84f of resonance frequency is small and stable, and that their unloaded Q is large.
Some dielectric ceramic compositions essentially comprising TiO2, BaOxe2x80x94TiO2 or the like are known, but they are difficult to industrialize as their temperature coefficient is large and their dielectric loss in a microwave zone is large.
Other dielectric ceramic compositions having a perovskite structure of, for example, Ba(Mg⅓Ta⅔)O3, Ba(Zn⅓Ta⅔)O3, Ba(Zn⅓Nb⅔)O3 or the like are known, but their dielectric constant is small. Therefore, for example, when they are formed into resonators usable in a microwave zone of from 0.1 to 5 GHz, the size of the resonators is inevitably large.
One object of the present invention is to provide a dielectric ceramic composition favorable for dielectric resonators, especially for those for use in a microwave zone of from 0.1 to 5 GHz.
Another object of the invention is to provide a dielectric ceramic composition having a high dielectric constant xcex5r, a high Q value, and a small and stable absolute value of the temperature coefficient xcfx84f of resonance frequency.
We, the present inventors have found that, of many constituent elements used in dielectric ceramic compositions, a specific ceramic composition comprising a combination of calcium, titanium, aluminium, niobium and oxygen attains the above-mentioned objects, and have completed the present invention.
Specifically, the invention provides a dielectric ceramic composition comprising a first compound of a general formula, aCaTiO3xe2x80x94(1xe2x88x92a)Ca(Alxc2xdNbxc2xd)O3 with 0.4xe2x89xa6axe2x89xa60.6.
The invention also provides a dielectric ceramic composition comprising the first compound as above and containing, as a second compound, at least one of zirconium oxide (ZrO2), manganese oxide (MnO2) and antimony trioxide (Sb2O3), in which the amount of the second compound is at most 2 parts by weight relative to 100 parts by weight of the first compound.